1. Field of the Invention
The present invention relates to optical systems, and, more particularly, to collimators wherein an optical fiber is fused directly to a lens.
2. Description of Related Art
The use of fiber lasers in industrial cutting and welding applications has grown, owing to the ever-increasing power output provided by laser manufacturers. This increase in power levels has created a need for collimators that can perform without performance degradation or failure under these conditions.
Standard collimator packages are limited in their power handling owing to the air space between the fiber and the lens. These collimator packages require both angle-polished fibers and lenses to prevent back-reflection to the source. Additionally, both these surfaces require anti-reflection coatings. While current technology provides low-reflection coatings (<0.25% per surface), at power levels approaching 100 W, there would still be 0.5 W reflected back into the system, owing to this interface.
This problem is further compounded by the fact that standard collimator packages use epoxy as the bonding mechanism for the fiber. Laser energy reflected back into the collimator from other sources such as the workpiece, aside from that owing to the air space, causes the epoxy to heat up. The high expansion of the epoxy can cause performance degradation as the epoxy expands and pulls the fiber with it. Additionally, even the highest-temperature epoxies can only handle less than 300° C. for any sustained period. Beyond that, the epoxy degrades and may burn off, causing catastrophic failure of the collimator.
The reflections caused at the air space interface can be eliminated through the use of a fused collimator. In a fused collimator the optical fiber is fused directly to a fused silica lens. This configuration eliminates the need to angle polish and coat the fiber and lens. The fusion allows the laser energy to pass from the fiber into the lens with less than −70 dB back-reflection.
For higher-power applications, however, the standard fused collimator package is insufficient. The fusion joint between the fiber and the pellet is strain-relieved using a high-temperature epoxy. As discussed above, reflections caused by the operating environment can heat the epoxy above its recommended use temperature, causing performance drift or catastrophic failure of the fusion joint.
Therefore, it would be desirable to provide a way of either eliminating or moving the epoxy strain relief away from the fusion joint.